The present invention relates to an arrangement for the contactless measurement of the concentration and the derivation of a mass flow rate of a moving material. More particularly, the present invention relates to an arrangement for the contactless measurement of a mass flow rate of a material moving through an electromagnetic field of known frequency and power based upon the magnitude of the electromagnetic energy reflected by the material as it passes through the field and the velocity of the material.
Disturbance sensors that utilize an electromagnetic signal of known frequency to determine the velocity, distance, or presence of a moving target object are known. Examples of some more well known disturbance sensors include those used in police and aircraft radars. These sensors rely on a change or shift between the frequency of an electromagnetic signal transmitted from the sensor and the frequency of that portion of the signal which is reflected by the moving target object. This change or shift in the frequency of a transmitted and reflected electromagnetic signal is referred to as a Doppler shift. An example of such a change or shift that is detectable at audible frequencies occurs when an audible source is active and moving relative to a person. The sound pitch is perceived to increase when the audible source is moving toward the person and to decrease when the audible source is moving away from the person. The magnitude of this frequency shift or change is proportional to the velocity of the moving object.
The present invention establishes that the concentration of a moving material can be measured based upon the amount of electromagnetic energy or power reflected by the material when it passes through a field of electromagnetic energy of known power. Applicant has observed that as the concentration of a material increases, the magnitude of electromagnetic energy that is reflected by the material also increases. The present invention further establishes that the flow rate of a material moving past a point can be determined by multiplying the mass of the material moving past the point by the velocity of the material. The mass, in turn, is equal to the volume of the material and air illuminated by the field divided by the concentration of the material.
The present invention combines the magnitude of electromagnetic energy reflected from a moving material with the Doppler shift frequency to produce a response related to the mass flow rate of the material. The invention subsequently utilizes this response along with user-supplied data relating to a particular material process flow to generate a linearized response related to the mass flow rate of the material.
Current mass flow rate meters that have sensors, such as antennas and impact plates, which are placed in a material process flow path have several disadvantages. Over time, material can build up on these intrusive sensors which impairs meter sensitivity. Also, such sensors require frequent adjustment because continual and repeated material impact eventually moves them out of calibration. In addition, moving material can impact an intrusive sensor in such a way that it is damaged and in need of repair or replacement. Furthermore, intrusive sensors are subject to changes in ambient conditions within a material process flow, such as temperature and humidity, which requires that a meter be recalibrated to the new ambient conditions or that the conditions of the material process flow be carefully monitored and adjusted. Finally, impact sensors can damage the material in a process flow.
The present invention addresses the above-described problems associated with intrusive mass flow rate meters by providing a contactless (i.e., non-intrusive) mass flow rate meter. The contactless mass flow meter of the present invention includes a transceiver that transmits an electromagnetic signal of known frequency and power across a material process flow. The transceiver detects the magnitude and Doppler shift of the electromagnetic signal that is reflected by material moving along the process flow as it passes through an electromagnetic field established by the signal. The transceiver then combines the magnitude of the reflected electromagnetic signal along with the Doppler shift between the frequency of the transmitted and reflected electromagnetic signals to generate an output signal related to the mass flow rate of the material. This signal has a magnitude substantially equal to the magnitude of the reflected electromagnetic energy and a frequency substantially equal to the difference between the frequency of the transmitted and reflected electromagnetic signals. This signal may be linear or non-linear.
The present invention further includes an amplifier electrically associated with the transceiver to amplify the transceiver output signal to a predetermined level for a predetermined frequency range so that the signal may be further processed. A user interface of the present invention allows the mass flow meter to be set up and calibrated for a particular material process flow as well as adjusted over time. A central processing unit of the present invention calculates a linearized output signal representative of the mass flow rate of the material, which is based upon the user supplied set-up, calibration, and adjustment data and the amplified transceiver output signal. The central processing unit then converts this linearized signal into a digital representation of the mass flow rate of the material. Circuitry of the present invention processes the digital central processing unit output signal to generate a signal related to the mass flow rate of the material.
In a preferred embodiment of the present invention, the digital central processing unit output signal is a pulse width modulated signal. The pulse width of this signal is related to the mass flow rate of the material such that the width of the signal increases with increased material flow rate. A circuit of this preferred embodiment converts the pulse width modulated signal into an analog current signal that is substantially linear through the range of mass flow rates. The magnitude of this current signal is related to the pulse width modulated signal such that the larger the width of the pulse, the higher the magnitude of the current signal.
In the same preferred embodiment, the central processing unit generates two output signals, one of which is indicative of the condition where the mass flow rate is below a user predefined minimum level and the other of which is indicative of the condition where the mass flow rate is above a user predefined maximum level.
The above-described user interface of the present invention allows the mass flow meter to be calibrated to the particular characteristics of a material process flow. The user interface of a preferred embodiment allows the amplification or sensitivity of the meter to be adjusted for a particular material process flow so that optimum amplifier gain occurs during maximum flow rate of the material. To achieve optimum gain, the gain of the amplifier may have to be adjusted up or down depending upon the characteristics of a particular process flow. The user interface of this preferred embodiment also allows calibration points to be set at various material flow rates so that the central processing unit can linearize the amplified transceiver output signal using interpolation techniques. The user interface of this preferred embodiment further allows a user to adjust the size of a central processing unit buffer that receives and stores amplified transceiver output process flow signals. Increasing the size of this buffer increases the number of amplified transceiver output process flow signals that are used by the central processing unit to generate a linearized signal representative of the mass flow rate of the material. The user interface of this preferred embodiment also allows the above-described minimum and maximum mass flow rates to be set and changed for those embodiments of the meter of the present invention which generate these signals. Finally, the user interface provides status information that allows a process flow to be monitored.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.